Here are two interesting articles from the Jakarta Post, where they know better about the terrain where it happened, and speculate as much as everyone over what might have happened and some really great stuff to feed your appetite for rumors and theories:
Mt. Salak: An airplane graveyard | The Jakarta Post
and over the weather over there by then:
Thick cloud covered Mt. Salak before Sukhoi crash | The Jakarta Post
Did they try to go under the weather rather than pass through? Still sounds like a very bad idea in that neck of the world.
They must have had a real mecanical problem degrading seriously they flight capability to want to (or not, but still) get in that s
t!